The present invention relates to a method for centrifugal spinning of textile yarn within a rotatable spinning centrifuge, typically an open-ended cylinder, commonly referred to as pot spinning. More particularly, the present invention relates to a method of pot spinning on a spinning machine with a plurality of spinning stations whereat a fibrous rope or other suitable continuous supply of spinnable fiber, typically and preferably in the form of a sliver or a roving, is drawn by means of a drafting device, is guided via a tubular reciprocating yarn guide into a rotating spinning centrifuge, is spun into a yarn and, while forming a rotating yarn leg as the yarn exits the guide, is deposited in the form of an annular spinning cake on the inner wall of the spinning centrifuge. The present invention further relates to a pot spinning machine, having a plurality of work stations, each of which has a centrifuge rotatable about a shaft and a reciprocable yarn guide for introducing into the centrifuge a drawn fibrous sliver received from a drafting device.
In pot spinning, a sliver is delivered from a sliver can and drawn in a drafting device, or a roving is delivered in the form of a speed frame bobbin, referred to collectively herein as a slubbing, is introduced into a rotating spinning centrifuge by means of a yarn guide reciprocable downwardly and upwardly within the centrifuge, is spun into a yarn, and is deposited as a so-called spinning cake on the inner wall of the spinning centrifuge.
More specifically, the slubbing delivered from the mouth of the yarn guide is transported by the action of an air flow rotating along with the spinning centrifuge to the inner wall of the spinning centrifuge and becomes fixed thereon centrifugally such that a moving yarn leg is created extending from the guide to the inner centrifuge wall and rotates around the centrifuge axis. The required twisting of the fibers of the sliver or roving necessary to form them into a yarn is imparted by means of the rotation of this yarn leg before it is deposited on the rotating inner surface of the centrifuge in the form of the spinning cake. At the end of a spinning cycle, e.g., after a predetermined amount of yarn has accumulated in the centrifuge, the yarn of the spinning cake which has been spun theretofore is rewound onto a rewinding tube introduced into the centrifuge. This rewinding process is initiated, for example, by pushing the rewinding tube forwardly into the centrifuge and into the path of the yarn leg. In the course of doing so, the rewinding tube grasps the rotating yarn leg coming out of the yarn guide by means of the leading edge of the tube, whereby the spinning cake deposited on the inner wall of the spinning centrifuge is then rewound onto the rewinding tube.
A yarn break can occur in the course of this rewinding process, resulting in a yarn body remnant remaining in the centrifuge after the rewinding of the yarn body onto the rewinding tube. A method and a device for restarting the rewinding process in pot spinning following such a yarn break are known from the later published patent application German Patent Publication DE 198 02 656. This document discloses the introduction of a special yarn loosening element into the centrifuge for grasping a yarn end of the yarn body remnant left in the centrifuge. Although yarn body remnants can be quite dependably removed from the spinning centrifuges by such a device, the occurrence and the presence of such yarn body remnants is often not noticed or noticed only very late.
Since such yarn body remnants also further reduce the already relatively limited receiving volume of the spinning centrifuges, it is important in the interest of the highest possible efficiency of a pot spinning machine to swiftly detect a yarn body remnant which has remained in the centrifuge, and to initiate appropriate counter-measures.
A method for pot spinning is known from German Patent Publication DE 195 23 835 A1, wherein the length of the rotation time of the yarn legs rotating in the spinning centrifuges is measured whereby a change of the length of the rotating time of the yarn leg occurring is immediately recognized and the already spun yarn body can be saved by introducing a rewinding tube.
It is furthermore known to detect the presence of a roving yarn introduced into the spinning centrifuge by means of a yarn sensor arranged between the drafting device and the reciprocable yarn guide tube. In the presence of the roving yarn, the yarn sensor provides an appropriate output signal. Here, the yarn sensor detects the movement of the roving yarn and provides an output signal which is proportional to the movement, preferably a noise signal. Such monitoring of the movement of the roving yarn is described, for example, in German Patent Publications DE 42 06 030 A1 or DE 42 06 031.
In case of a yarn break at a spinning station, an interruption of the material feed takes place as a rule. Thus, delivery of roving yarn is interrupted by means of a stop device acting on the slubbing. Such slubbing stop devices arranged in the area of the drafting devices are known from German Patent Publication DE 38 22 930 A1, for example.
Based on the above mentioned prior art, it is an object of the present invention to provide a method and a device which assures in a simple and cost-effective manner that the individual spinning centrifuges of a pot spinning machine are in an optimal state at the start of the spinning cycle, in particular that the spinning centrifuges are empty without any spinning cake remnants.
This object is achieved in accordance with the present invention by a method wherein all spinning centrifuges of the pot spinning machine are checked for the presence of possible yarn body remnants at the start of a spinning cycle, which makes it possible to dependably avoid that spinning centrifuges which having a yarn remnant remaining in the spinning centrifuge, and hence would produce poor spinning cops, are placed into the normal spinning process.
More specifically, the present method contemplates that the rotary frequency of the yarn legs of the individual work stations of the pot spinning machine is determined at the start of a spinning cycle of the pot spinning machine, and the rotary frequencies for each work station is compared with a predetermined set value. Thus, possible yarn body remnants in one or several of the spinning centrifuges of the work stations can be immediately detected because of the appearance of differences in the rotary frequency in comparison with the set value. In the course of measuring the rotary frequency of the yarn leg, the fact is taken into account that piecing takes place on the possibly still present yarn body remnant and that the reduction in the free radius as a result of this also leads to a reduction of the rotary frequency of the yarn leg.
More specifically, in a centrifuge rotating at a constant rotary frequency, a yarn body remnant left in the spinning centrifuge immediately leads to a lower rotary frequency of the respective yarn leg, based on the equation:
fG=fZxe2x88x92VL/2xcfx80*r
wherein fG represents the rotary frequency of the yarn leg, fZ represents the rotary frequency of the centrifuge, VL represents the delivery speed of the yarn, and r represents the free radius of the centrifuge. It is therefore possible by means of an appropriate evaluation of the rotary frequency of the yarn legs to draw a direct conclusion regarding the presence of a yarn body remnant in the respective spinning centrifuge, which reduces the free radius.
In an advantageous embodiment of the invention, the rotary frequency of the rotating yarn leg is measured by means of a yarn sensor detecting the movement of the yarn. That is, a yarn sensor is arranged between the drafting device and the reciprocable tubular yarn guide to detect a yarn movement occurring in the area of the yarn sensor which corresponds to the rotary frequency of the yarn leg in the spinning centrifuge.
According to a further aspect of the invention, this yarn movement corresponding to the rotary frequency of the yarn leg is filtered out of the noise signal, which is detected by means of the yarn sensor and represents the movement of the yarn. For this purpose, the noise signal is conducted over a filter stage, for example, which detects a frequency signal based on the rotary frequency of the yarn leg. Processing of this frequency signal, for example by means of a fast Fourier transformation or the like, leads to frequency lines located in a defined spectral range, which can be unequivocally assigned to clearly defined free radii within the centrifuge.
By means of comparing these spectral lines with set values which are to be expected with empty centrifuges, the presence of a yarn body remnant can be immediately determined, so that appropriate counter-measures can be initiated. Since the free radius of an empty centrifuge is known because of the known geometric dimensions, the determination of a set value to be expected is possible in a simple manner.
In an advantageous feature of the invention, it is further provided that the rotary frequency of the yarn leg at each work station is determined simultaneously at all work stations. An unequivocal association of this data with each respective individual spinning station takes place in a measuring and evaluation unit, whereby it is possible by means of a comparison of the respective rotary frequencies from the work stations with the preset value to immediately determine whether and in which of the spinning centrifuges a yarn body remnant could possibly still be present. Since it is assumed that a yarn body remnant occurs seldom, and even more seldom at the same time at several work stations, the detected numbers of revolution of the yarn legs can also be compared with each other, so that it is possible to omit the provision of an external set value. In effect, the spinning stations not showing a yarn body remnant provide an internal set value.
Upon detecting a yarn body remnant in a spinning centrifuge, an appropriate control signal is immediately issued to the slubbing stop device of the respective work station via the evaluation unit, whereby the further delivery of roving yarn is stopped at the respective work station.
The objective of the invention is furthermore attained by providing the pot spinning machine with a sensor arrangement which makes it possible to detect at least one of the physical values appearing during a spinning cycle. The detected value is compared with a predetermined set value, for example in a work station computer or in a central spinning machine computer, and conclusions regarding the load status of the individual spinning centrifuges are drawn from the result of this comparison.
In this invention, the sensor arrangement is preferably designed as a yarn sensor, located between the drafting device and the yarn guide, which detects the presence of the slubbing. Because a filter stage is assigned to this yarn sensor, a signal corresponding to the rotary frequency of the yarn leg can be filtered out of the output signal of the yarn sensor and the signal may therefore be used for comparison with a set value signal in an evaluation circuit.
In this manner, a detection and evaluation of the rotary frequency of the yarn legs rotating with the spinning centrifuges can take place without extensive structure or structural modifications to the spinning machine, which might possibly require additional structural space. More specifically, only a filter stage, and a comparator which compares the signals, are required for modifying an already existing device such that, through the measurement of the rotary frequency of the yarn legs, conclusions can be immediately drawn regarding the possible presence of a yarn body remnant in one of the spinning centrifuges.
According to a further aspect of the invention, the pot spinning machine has a central control device, in which the signals provided by the individual yarn sensors are evaluated in regard to the detected rotary frequency of the yarn legs. In this manner, it is possible advantageously to perform a comparison with the set value in a compact unit, wherein the set value need only be made available once for all spinning stations. It is furthermore possible in an alternative embodiment to perform a comparison of the rotary frequency of the yarn legs of the individual work stations in respect to each other in a simple way by means of the control device.
Further aspects, features and advantages of the present invention will be explained in greater detail and will be understood form the following disclosure of an exemplary embodiment represented in the accompanying drawings.